1. Field of the Invention
The invention generally relates to lifting aids and, more particularly, to a failsafe device for raising/lowering articles.
2. Description of the Prior Art
There are devices known in the art for vertically raising/lowering an article, such as a monitor, a bicycle, a kitchen cabinet, a multi-level garment holder, or the like. These items normally rest on a bracket mounted on a wall, ceiling, or beam, or they may be mounted on a self-supporting vertically arranged framework. Some of these devices provide additional floor space under the raised article when the stored item is not needed. All include some form of hoisting means. Most of these devices are relatively expensive to manufacture, and are normally not sufficiently simple or safe enough in operation to also be used by children.
In U.S. Pat. No. 152,635 a pulley-block is disclosed in which the brake block follows the contour of the pulley. A spring biases the brake block to the cord-locking position so that the dropping of the article is arrested soon after the cord is released. However, to ensure locking of the cord it needs to be moved to an inclined position. The maximum stopping force is a function of the spring and the inclination of the cord to be controlled. If the spring is strong, however, high friction is applied on the cord in both directions. Additionally, to lower the article an additional cord must be pulled to remove the block from the braking position while the user simultaneously holds on to the main cord. Otherwise, the article would go into free fall and possibly cause injury or damage to the article. If the article is to be lowered a substantial distance the user would need to hold the brake block releasing cord with one hand and try to control the main cord with the other hand. This could be very difficult and inconvenient and could best be achieved with the aid of a second person who holds the releasing cord while the user uses both hands (hand-over-hand) to lower the article.
In U.S. Pat. No. 723,231 a pulley block is disclosed which also requires that the cable be manually inclined by the user to stop the movement of the cable, the degree of friction for arresting the cable being a function of the force with which the cable is inclined by the user. Release of the cable would result in free fall of the article.
In U.S. Pat. No. 826,727 a cloths line pulley is disclosed in which the cable is wedged between a pulley and a pawl. The greater the pressure on the pawl the greater the binding action. However, the pawl must be manually flipped to provide to described operation to lock the movement of the cord in one direction or the other.
In U.S. Pat. No. 916,091 a pulley and rope or cable holder is disclosed in which dual cams must be manually moved to provide locking action in either direction. A further pulley usable for clothes lines and lock for cables is disclosed in U.S. Pat. No. 1,107,934 in which a cam locks the cable when the cable is slack. Adjustments may be made depending on how tight or loose the cable is to lock with clothing on.
In U.S. Pat. No. 1,167,295 a pulley block is disclosed which requires lateral movements of the cable to inclined positions for locking the cable and, therefore, is similar to many of the aforementioned designs.
In U.S. Pat. No. 2,867,875 a cable clamp is disclosed in which the cable must be manually moved in relation to a stud on a pivoted lever to effect locking by wedging the cable against a jaw that is fixed during operation. Therefore, the device requires pulling of the cable laterally. While the cable may also be pulled downwardly there is a danger that the cable may re-engage if the user is not careful. While this device includes a cam it is in the form of a movable jaw that is fixed even if adjustable. Therefore, there is no element that tends to move toward a cable except for manual movements prior to use to accamodate the size of the cable.
In U.S. Pat. No. 5,615,865 a device is described that automatically engages and disengages a pawl and a lifting mechanism using the same. However, special stops are required to be placed on the cable. If the load is lifted and the pulling force is released the pawl engages the cable to prevent the load from falling. However, a stop on the cable must be moved to a position which tilts the lever to disengage the paws to allow the load to be lowered.
Clearly, the prior art devices frequently rely on special manipulations or movements by the user to arrest the downward movements of the article supported on a cable. However, such designs are not failsafe since error by the user could cause the article to drop uncontrollably. This may cause damage or injury. Additionally, with devices of the type under discussion a cable must be arrested immediately when released since the article may otherwise go into free fall and accelerate to a high velocity resulting in a high momentum. This makes it more difficult to stop the article instantaneously without creating substantial stress upon the cable and on the support surface that supports the device. This could result in damage to the support surface and, in fact, actually cause the device to separate from the support surface and, again, cause possible injury to personnel or damage to property.